 
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
|
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
68.37.254.189
In Reply to: RE: Eico HF-35 and Knight KB-85 mods posted by Nebulix on July 14, 2013 at 20:41:35
Run each LED off of the AC mains. A UF4007 in series with each LED takes care of PIV considerations. A current limiting resistor in series with each diode string ensures against diode overheating.
Eli D.
Follow Ups:
Thank you Eli. I'll try that tomorrow. Sounds simple enough.
Now I've been searching through the forum about PIO threads.
If anyone knows the Eico HF-35 (or any of the similar HF-series) there are two coupling capacitors C5 and C7, to the final stage. The original spec was 0.1 uF @ 600V. I've replaced them with modern film capacitors but would like to go with Russian PIOs. For some reason, the HF-35 specifies 0.1 uF, but other models such as the HF-60 use 0.25 uF for coupling. Is this a preferable value e.g. more bass? More? (The PIOs are 0.22 uF, but I see one guy put 1.0 uF in this place.)
Also, there's a capacitor C4, grounded from the grid of the phase inverter. The original was a molded 0.25 uF @ 400V. I've replaced it also with a film cap. I see that Stu replaces this one with a PIO. Is this capacitor actually considered to be in the signal path i.e. is it worth me replacing it with a PIO?
Thanks in advance,
Duncan Mc.
To maximize the service life of old stock 5AR4/GZ34s and ensure reliable operation of Sovtek 5AR4s (best among current production), install the SS diode tweak as shown in the uploaded graphic.
While the graphic shows 1N4007s, use UF4007s, which generate FAR less switching noise. Yes, the vacuum rectifier blocks "sand" diode switching noise from entering the B+ rail. However, less noise, from the outset, has to be better.
Eli D.
Can the same hybrid diode setup as shown on the sketch for the 5ar4 which is identified as a 5ar4graetz in Duncan PSUDII be used for the 5u4gb, what would be the differences.
Just want to add a schematic of what I ask in the previous message
So just to clarify, this mod would protect against a dead short in the tube, as the sand diode would kick in and protect the caps from AC. Is there any other advantage? Is the diode augmenting the tube in any way?
Someone mentioned earlier about running SS rectifiers in parallel with the tube rectifier. I'm not sure if they were referring to this mod.
Eli, thank you for this. I was going to ask you guys about the ss diode mod, and here it is. Great drawing.
So this ends up like two rectifiers in series, right? It doesn't actually bypass the tube, it augments it.
I've ordered a bunch of FREDs so I'll try it. Seems simple enough and I've had a lot of trouble with 5AR4s and heard the Sovteks were the best. I've got a couple of Shuguangs in the mail. We'll see how they fare.
Duncan
When it comes to any of the Eicos and if you left in the GZ34 rectifier,you want pay attention to the power supply more than anything.
First and foremost you want to put an all film cap power supply in those amps.Its very easy to do and its makes a MONUMENTAL difference and I am not exaggerating..
You can put a a pair of 30uf polys right off the gz34 if you are using a mullard GZ34 or if you put in a pair of UF4007s with a rectifier tube.
You can put one on the top hole of the first filter cap and glue one underneath.The other filter cap you put in a pair of 35uf@500v..One on top and one underneath the chassis.They are the smaller black CDEs off to the right next to the brown nippon Chemicons..You can also get a 51uf@600v poly can and I did that on my hf60s..Don't worry about 60uf on a GZ34.The Mullards can take it and they are slow to charge up to the tube will be fine especially with the diodes..You don't have to put those in but the polys are the charmer.
Edit..You don't have to put an all film cap power supply in however,it is very easy and economical to do and the performance gains are wonderful..You at least want to put a 35uf poly after the rectifier.
Edits: 07/15/13
Thanks so much Michael. All poly would be sweet. Didn't think they made them that big.
I'm going to email you directly and we can chat. I'd be interested in sourcing the big black caps. Also still working on the KB-85 circuit boards. I'll be doing up a batch of bare boards shortly and I'll send you a coulple. I've ordered some thick blank boards and more etchant.
Cheers,
Duncan Mc.
Post a Followup:
| FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
||||||||||||||
This post is made possible by the generous support of people like you and our sponsors:
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2025, Audio Asylum, all rights reserved ]
